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201.
Heather E. Golden Elizabeth W. Boyer Michael G. Brown S. Thomas Purucker René H. Germain 《Journal of the American Water Resources Association》2009,45(4):945-962
Abstract: Nitrate‐nitrogen (NO3‐N) concentrations in stream water often respond uniquely to changes in inter‐annual conditions (e.g., biological N uptake and precipitation) in individual catchments. In this paper, we assess (1) how the spatial distribution of NO3‐N concentrations varies across a dense network of nonnested catchments and (2) how relationships between multiple landscape factors [within whole catchments and hydrologically sensitive areas (HSAs) of the catchments] and stream NO3‐N are expressed under a variety of annual conditions. Stream NO3‐N data were collected during two synoptic sampling events across >55 tributaries and two synoptic sampling periods with >11 tributaries during summer low flow periods. Sample tributaries drain mixed land cover watersheds ranging in size from 0.150 to 312 km2 and outlet directly to Cayuga Lake, New York. Changes in NO3‐N concentration ratios between each sampling event suggest a high degree of spatial heterogeneity in catchment response across the Cayuga Lake Watershed, ranging from 0.230 to 61.4. Variations in NO3‐N concentrations within each of the large synoptic sampling events were also high, ranging from 0.040 to 8.7 mg NO3‐N/l (March) and 0.090 to 15.5 mg NO3‐N/l (October). Although Pearson correlation coefficients suggest that this variability is related to multiple landscape factors during all four sampling events, partial correlations suggest percentage of row crops in the catchments as the only similar factor in March and October and catchment area as the only factor during summer low flows. Further, the strength of the relationships is typically lower in the HSAs of catchment. Advancing current understanding of such variations and relationships to landscape factors across multiple catchments – and under a variety of biogeochemical and hydrological conditions – is important, as (1) nitrate continues to be employed as an indicator of regional aquatic ecosystem health and services and (2) a unified framework approach for understanding individual catchment processes is a rapidly evolving focus for catchment‐based science and management. 相似文献
202.
Monitoring morphological and vegetation changes and flow events in dryland river channels 总被引:1,自引:0,他引:1
Hooke JM 《Environmental monitoring and assessment》2007,127(1-3):445-457
Monitoring of impacts of floods in river valleys of dryland regions has become important with the onset and threats of desertification
and is likely to become even more vital with predictions of increased effects of climate and land use change. It is also needed
in order to conform to requirements of the EU Water Framework Directive. Monitoring in such regions sets particular challenges.
This paper explains a system of low-cost monitoring of changes in morphology, vegetation and sediment cover in channels and
valley floors of ephemerally flowing streams. It has been applied in SE Spain for 10 years and has proved very effective.
In particular, the use of simple crest-stage recorders for measuring flow height and the use of real-time differential GPS
for rapid and accurate survey and for relocating points have proved very valuable. Part of the monitoring is focused on the
interaction of plants and channel processes. Small changes in and around vegetation associated with flow events have been
detected by a combination of quadrat surveys and cross-profiling of the channel. A range of flow events has been measured
over the period of monitoring, demonstrating their differing effects and the varying sensitivity and responsiveness of different
sites. The sporadic occurrence of flood events in such an environment means that a strategy of monitoring several sites and
of continuation over many years has great benefits. 相似文献
203.
Recognition and understanding of landscape dynamics as a historical legacy of disturbances are necessary for sustainable management
of forest ecosystems. This study analyzed spatial and temporal changes in land use and land cover patterns in a typical mountain
watershed in the Gumushane district along the Northeastern part of Turkey. The area is investigated by comparing LANDSAT images
from 1987 to 2000 and evaluated the temporal changes of spatial structure of forest conditions through spatial analysis of
forest cover type maps from 1971 and 1987 using GIS and FRAGSTATS™.
The results show a general decreasing trend in area of natural land cover types including broadleaf and conifer forests as
well as coppice between 1971 and 1987 (0.54%, respectively). In contrast, between 1987 and 2000 this natural land cover types
show increasing trend (1.6%). In parallel with forest dynamics, the area of managed land including lowland and upland agricultural
areas, rangelands and grasslands increased during the first period and decreased during second period. In terms of spatial
configuration, Gümüşhane forests aren’t generally fragmented by intensive forest utilization in the latter periods. This is
partially due to out-migration of rural population in Gümüşhane. Nevertheless, land use pattern significantly changed over
time depending on a few factors such as unregulated management actions, social pressure and demographic movements. The study
revealed that demographic movements have a major effect on landscape dynamics. 相似文献
204.
近年来江苏省海岸带土地利用/覆被变化时空动态研究 总被引:1,自引:0,他引:1
海岸带是陆海生态系统交错带,具有重要的经济与生态价值,其生态环境具有脆弱性特征。海岸带的开发利用使其地区生态环境发生变化,而土地利用/覆被变化是地区生态环境变化的重要组成部分和主要原因之一。取1980、2000、2005、2008年4个时相的TM遥感影像为数据源,通过土地利用结构、土地利用多样性以及土地利用程度指数分析江苏省1980年以来海岸带土地利用/覆被变化的时空动态特征,揭示地域差异与梯度分异特征。研究结果表明:(1)江苏省海岸带土地利用结构表现为生态用地占比高,城镇与农村居民点占比低的特征。1980年以来,不同土地利用类型数量不断变化而结构相对稳定;类型趋于多样化且利用强度增加。(2)江苏省海岸带土地利用存在地域差异特征。土地利用结构存在不同模式且变化相对稳定;土地利用程度在南北方向上存在高 低 高分布特征,但逐步被打破。(3)江苏省海岸带土地利用在陆海方向上存在梯度特征。土地利用多样性陆海方向呈现低 高 低模式,土地利用强度陆海方向呈现高 中 低模式。土地利用多样性高值区逐步向海岸带中部移动;海岸带各缓冲区土地利用程度分异逐步增大。以射阳河口作为分界点,南北地区梯度规律存在差异性 相似文献
205.
We report on a revisit in 2009 to sites where vegetation was recorded in 1967 and 1970 on Disko Island, West Greenland. Re-sampling
of the same clones of the grass Phleum alpinum after 39 years showed complete stability in biometrics but dramatic earlier onset of various phenological stages that were
not related to changes in population density. In a fell-field community, there was a net species loss, but in a herb-slope
community, species losses balanced those that were gained. The type of species establishing and increasing in frequency and/or
cover abundance at the fell-field site, particularly prostrate dwarf shrubs, indicates a possible start of a shift towards
a heath, rather than a fell-field community. At the herb-slope site, those species that established or increased markedly
in frequency and/or cover abundance indicate a change to drier conditions. This is confirmed both by the decrease in abundance
of Alchemilla glomerulans and Epilobium hornemanii, and the drying of a nearby pond. The causes of these changes are unknown, although mean annual temperature has risen since
1984. 相似文献
206.
A 30-year series (1978–2007) of photographic records were analysed to determine changes in lake ice cover, local (low elevation)
and montane (high elevation) snow cover and phenological stages of mountain birch (Betula pubescens ssp. czerepanovii) at the Abisko Scientific Research Station, Sweden. In most cases, the photographic-derived data showed no significant difference
in phenophase score from manually observed field records from the same period, demonstrating the accuracy and potential of
using weekly repeat photography as a quicker, cheaper and more adaptable tool to remotely study phenology in both biological
and physical systems. Overall, increases in ambient temperatures coupled with decreases in winter ice and snow cover, and
earlier occurrence of birch foliage, signal a reduction in the length of winter, a shift towards earlier springs and an increase
in the length of available growing season in the Swedish sub-arctic. 相似文献
207.
The changes in the vascular plant flora of Tasiilaq, low arctic Southeast Greenland, between around 1900 and 2007 were studied
by comparing the data from historical literature with those of the field observations performed between the late 1960s and
2007. Since 1900, the percentage of widely distributed arctic species distinctly decreased, whereas that of the low arctic
species somewhat increased, and boreal species hardly increased. Vegetation monitoring revealed minor changes and showed that
several thermophilous and xerophilous species increased between 1968/1969 and 2007, whereas some hygrophilous species decreased.
Repeated vegetation mapping of a shallow pond revealed conspicuous changes suggesting increased evaporation/precipitation
ratios associated with environmental warming up and decreasing snow accumulation in winter, in line with results of previous
investigations. In spite of climate warming, expansion of the town and increasing human impact, flora and vegetation on the
whole appeared rather stable during the last 40 years without invading species or introductions. 相似文献
208.
土地利用/土地覆盖是生态环境系统的组成部分,它的变化是区域生态环境演变的直接反映和结果,它是区域生态环境演变的一个重要因素。运用RS/GIS技术,采用土地利用类型覆盖率作为评价因子,参考国际和国内各省的土地利用类型覆盖率制定评价标准,对伊犁河谷生态环境进行模糊综合评价。得出伊犁河谷生态环境质量属"优"的面积覆盖率占伊犁河谷总面积的73.2%;生态环境质量为"良"的县市面积覆盖率占伊犁河谷的26.3%。伊犁河谷生态环境总体较好,局部较差。伊犁河谷各县市的耕地面积覆盖率、建设用地覆盖率和草地面积覆盖率是各县市生态环境状况差异的主要原因。该方法与其他方法比较,所得的评价结果比较一致,结论符合实际状况,且有计算简便快捷等优点,方法可行,具有一定的可靠性和理论价值。 相似文献
209.
210.
Human alteration of the landscape has an extensive influence on the biogeochemical processes that drive oxygen cycling in streams. We estimated trends from the mid-1990s to 2003, using the seasonal Mann-Kendall's test, for percent saturation dissolved oxygen (DO), chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN), and ammonia-nitrogen (NH(3)-N) for 12 sites in the Rock Creek watershed, northwest Oregon, USA. In order to understand the influence of landscape change, scale, and stormwater runoff management on dissolved oxygen trends, we calculated land cover change through aerial photo interpretation at full-basin, local (near sample point) basin, and 100m stream buffer scales, for the years 1994 and 2000. Significant (p < or = 0.05) trends occurred in DO (increasing at five sites), COD (decreasing at seven sites), TKN (decreasing at five sites, increasing at one site), and NH(3)-N (decreasing at one site, increasing at one site). Significant land cover change occurred in agricultural land cover (-8% for the entire basin area) and residential land cover (+10% for the entire basin area) (p < or = 0.05). Correlation results indicated that: (1) forest cover negatively influenced COD at the full basin scale and positively influences NH(3)-N at local scales, (2) residential land cover influenced oxygen demand variables at local scales, (3) agricultural land cover did not influence oxygen demand, (4) local topography negatively influenced TKN and NH(3)-N, and (5) stormwater runoff management infrastructure correlated positively with COD at the local scale. This study indicates that landscape factors influencing DO conditions for the study streams act at multiple scales, suggesting that better knowledge of scale-process interactions can guide watershed managers' decision making in order to maintain improving water quality conditions. 相似文献